Add footer with CHNS.tech credit and Buy Me a Coffee button

Adds a green footer (matching nav colour) to all authenticated pages
with a "Created by: CHNS.tech" link and a styled BMC button. CSP updated
to allow buymeacoffee CDN domains.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

nginx/html/css/style.css

@@ -23,6 +23,9 @@ body {
     background: var(--bg);
     color: var(--text);
     line-height: 1.5;
+    min-height: 100vh;
+    display: flex;
+    flex-direction: column;
 }
 
 a { color: var(--green); text-decoration: none; }
@@ -75,6 +78,8 @@ a:hover { text-decoration: underline; }
     max-width: 980px;
     margin: 0 auto;
     padding: 2rem 1.5rem;
+    flex: 1;
+    width: 100%;
 }
 
 h1 { font-size: 1.6rem; margin-bottom: 1.5rem; }
@@ -414,3 +419,45 @@ td input[type="date"] {
     padding: 0 0.25rem;
     line-height: 1;
 }
+
+/* ── Footer ──────────────────────────────────────────────────────────────── */
+.site-footer {
+    background: var(--green);
+    color: rgba(255,255,255,0.85);
+    padding: 1rem 1.5rem;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    gap: 1.25rem;
+    flex-wrap: wrap;
+    font-size: 0.9rem;
+    margin-top: auto;
+}
+
+.site-footer a {
+    color: #fff;
+    font-weight: 600;
+    text-decoration: none;
+}
+
+.site-footer a:hover {
+    text-decoration: underline;
+}
+
+.bmc-btn {
+    display: inline-block;
+    background: #d4850a;
+    color: #000 !important;
+    font-family: Arial, sans-serif;
+    font-size: 0.8rem;
+    font-weight: 700;
+    padding: 0.3rem 0.75rem;
+    border-radius: 6px;
+    border: 1px solid rgba(0,0,0,0.3);
+    white-space: nowrap;
+    text-decoration: none !important;
+}
+.bmc-btn:hover {
+    background: #c07609;
+    text-decoration: none !important;
+}